/**
 * 浮动球
 * @param {String} tag_id html标签ID
 */
function float_box(tag_id) {
  //获取元素
  var dv = document.getElementById(tag_id);
  var x = 0;
  var y = 0;
  var l = 0;
  var t = 0;
  var isDown = false;
  //鼠标按下事件
  dv.onmousedown = function(e) {
    //获取x坐标和y坐标
    x = e.clientX;
    y = e.clientY;

    //获取左部和顶部的偏移量
    l = dv.offsetLeft;
    t = dv.offsetTop;
    //开关打开
    isDown = true;
    //设置样式
    dv.style.cursor = 'move';
  }
  //鼠标移动
  window.onmousemove = function(e) {
    if (isDown == false) {
      return;
    }
    //获取x和y
    var nx = e.clientX;
    var ny = e.clientY;
    //计算移动后的左偏移量和顶部的偏移量
    var nl = nx - (x - l);
    var nt = ny - (y - t);

    dv.style.left = nl + 'px';
    dv.style.top = nt + 'px';
  }
  //鼠标抬起事件
  dv.onmouseup = function() {
    //开关关闭
    isDown = false;
    dv.style.cursor = 'default';
  }
}

module.exports = float_box
